This invention relates generally to a device for the detection of droplets of a chemical agent.
More specifically, this invention relates to a device for the detection of chemically active liquid droplets falling upon a surface and to a method for its use.
The chemical warfare capabilities of potential adversary nations is well documented. This potential threat comprises a broad array of chemical weapons including artillery, multiple rocket launchers, missiles, bombs and spray tank type chemical agent delivery systems. In fact, some of these chemical weapons have been used in localized foreign conflicts.
A wide variety of chemical agents are known to be in the arsenals of other nations. The principal threat agent is considered to be the nerve agent Soman, commonly referred to as GD. Soman and similar nerve agents such as Sarin and Tabun are commonly referred to as nerve gases but this is something of a misnomer. All are liquids with a relatively high boiling point and a relatively low vapor pressure. Soman, for example, has a normal boiling point of 167.degree. C.
Munitions designed to deliver nerve and other chemical agents typically produce a rain of liquid droplets which fall to the ground. Size of the droplets formed by the various delivery systems varies greatly. Artillery and small rocket munitions produce droplet clouds with droplet mass median diameters of about 150 microns. Aircraft sprays typically produce droplets of about that same size. Chemical agents delivered by bombs may have a mass median droplet diameter of 1000 to 1,500 microns and missiles may deliver even larger droplets; up to 3,000 microns. As can be appreciated, a detector having the capability of providing the earliest possible warning must respond to a very broad range of droplet sizes; from about 50 to 5,000 microns.
Chemical warfare agents such as the nerve agents produce casualities in several ways. If troops are in the fall out area as the droplets rain to the ground, then direct contact with the agent occurs resulting in casualties from percutaneous absorption of the liquid agent. Troops entering a contaminated area also are exposed to direct contact with the liquid agent again resulting in percutaneous absorption. As the agent evaporates a vapor hazard is created which may result in casualties by inhalation. It is of utmost concern that detection and warning of a chemical agent attack be as early as possible. That requires the capability of detecting the fall of agent droplets as well as detecting the presence of vapor in an area.
Currently, there are only two automatic detection and alarm devices available to our troops in the field. One, the M8-E1 alarm is used by the Army and Marines. The other, the IDS alarm, is used by the Air Force and Navy. Neither of these alarms can detect droplets having a mass median diameter above about 50 microns as both draw in an air sample and require that the agent be in vapor form for detection.
Several improved detector and alarm systems are presently under development. Only one of these, the Automatic Liquid Agent Detector System (ALADS), will have a droplet detection capability. The ALADS detector relies upon the impaction of droplets upon a detector plate comprising a conducting circuit whose characteristics are changed as the agent droplet dissolves a conducting matrix. This detector is sensitive only to droplets having a diameter greater than about 200 microns.
There are important civilian, as well as military, needs for a device having the capability of detecting the fall of chemically active agents. Among the most important of these civilian needs is the monitoring of agricultural pesticide and herbicide spray applications. Civilian applications of such detecting devices can in some instances, as for example the application of certain pesticides, use the same detection system as do the military devices.
Although there has been a long recognized need for a device capable of detecting the fall of chemically active liquid droplets, no practical system for so doing has yet been devised. Ideally, such a system would have the capability of detecting both droplets and vapor; would operate dependably over a large temperature range; would be simple in construction and would be dependable in operation.